1. Field of Invention
This invention is a supplemental fuel system for an internal combustion engine with more than one cylinder. Under normal operating conditions, the engine receives a substantial portion of its fuel from a primary fuel system, this primary system typically using carburetion or fuel injection. This supplemental fuel system provides fuel to the engine in addition to that supplied by the primary system. The quantity of supplemental fuel supplied to each cylinder is varied depending on the position of a valve and the size of an orifice in a fuel nozzle to each cylinder. This supplemental fuel system provides the functions of cold engine starting and enrichment until the engine warms to its normal operating temperature, and by adjusting relative fuel flow between cylinders, it is also useful as a tuning mechanism for the primary fuel system, especially at low engine speeds.
2. Description of Prior Art
Fuels used commonly in internal combustion engines, in a normal operating fuel/air mixture ratio, are not easily ignited when cold. When cold, the fuel/air ratio must be enrichened, supplying more fuel in relation to air than would normally be used in a warm engine, to allow ignition by an ignition source such as a spark plug. Therefore, many starting and enrichment systems have been developed which are used to provide extra fuel to the engine for starting and initial cold operation.
One method of starting and subsequent enrichment used with a carburetor is a choke, which is a second throttle plate positioned before a main throttle plate; closing the choke throttle increases the vacuum seen by the fuel outlets in the carb bore which causes additional fuel to flow to the engine. The choke throttle is normally completely closed for initial starting which provides maximum supplemental fuel flow, and is gradually opened during the engine warming process to gradually diminish the supplemental fuel. This system is well known in the art.
Another method of providing supplemental fuel for cold operation used with carburetors is called an enrichment circuit. This system uses an air passage which bypasses the throttle valve, the air flow through this air passage being regulated by an operator controlled plunger. Fuel from a carburetor float bowl enters this air passage through a fuel orifice, or jet, when the plunger is opened allowing air flow in the passage. The plunger normally is provided with a mechanism to allow the operator to place it in a fully open position providing maximum fuel flow for starting, and a partially open position which provides less additional fuel for enrichment after starting but before the engine has fully warmed. This system is also well known in the art.
Another system used for starting, both with carburetors and with fuel injection, uses a manually operated primer pump in its operation. The suction side of the primer pump is connected to a source of fuel, its pressure side is connected to fuel nozzles commonly placed in the throttle bore, and activating the pump causes fuel to enter the engine for starting. A crude form of enrichment for use after engine starting but before complete warming involves continued intermittent operation of the primer pump, providing additional xe2x80x9csquirtsxe2x80x9d of fuel to the engine while running. This system is somewhat unsatisfactory, however, since continual operator attention is required. Also, insufficient pumping allows the engine to quit running, while too much pumping causes the engine to flood. This system is also well known in the art.
Carburetors normally have several fuel circuits to provide the proper fuel flow at all engine operating conditions. Specifically, an engine operated at low speed and load requires a richer mixture than when run at normal operating speed and load. A carburetor circuit supplying fuel primarily for low speed engine operation is called a pilot circuit. This pilot circuit has a fuel passage with a restricting orifice, or pilot jet, connecting the carburetor float bowl to the venturi bore on the engine side of the throttle plate. By so positioning the fuel passage, a high vacuum is placed across the pilot jet at small throttle openings, but a decreased vacuum exists at larger throttle openings. This causes the pilot jet to deliver more fuel at low throttle openings than at higher throttle openings, hence the pilot circuit is able to provide the richer fuel mixture required by the engine at small throttle openings. This pilot circuit is well known in the art.
The pilot system in a carburetor is normally tuned by two methods. The first is simply changing the pilot jet; installing a jet with a small orifice provides a relatively lean mixture, a jet with a larger orifice provides a relatively richer mixture. In addition to changing the pilot jet, the pilot circuit also normally includes an idle mixture screw to modify fuel delivery. This idle mixture screw typically adjusts the needle position in a needle valve, and can take two forms, a fuel screw or an air screw. When the idle mixture screw is a fuel screw, the fuel screw adjusts a needle valve which controls a fuel feed circuit which parallels the pilot jet; opening a fuel screw will provide more fuel to the engine. When the idle mixture screw is an air screw, the air screw adjusts a needle valve which acts as an air bleed in the fuel passage supplying the pilot jet; opening an air screw will cause a decrease in fuel delivery by the pilot circuit. Both of these idle mixture screws are well known in the art.
Tuning the pilot circuit of a carburetor is not as easy as it would first appear, however. pilot jets are normally inside the carburetor, and changing them requires carburetor disassembly. The fuel or air screws are located on the carburetor, and the vehicle must normally be stopped to perform their adjustment. Also, the fuel or air screws are sometimes in locations which are difficult to access, and carburetor removal is sometimes required to adjust the screws.
Fuel injection systems also must provide the functions of starting and cold engine enrichment. Sometimes a primer system described above is used, or sometimes this function is programmed into the fuel injection computer. Also, the fuel enrichment at low engine speeds is normally programmed into the computer, and changing this low speed fuel delivery normally requires computer re-programming. Changing computer programming to adjust these fuel parameters is difficult and normally not within the skill level of the operator.
The applicant has a co-pending application 09/550774 for a mechanical fuel injection system which uses an injection pump installed on each engine cylinder, the pumps being driven by cylinder pressure pulses. For cold starting and enrichment a primer was used, and the pumps have a low-speed fuel adjustment screw. Starting and enrichening the system with the primer was not entirely satisfactory. Because of the nature of the operation of the injection pumps, often one pump would begin pumping fuel and the other would not, requiring stopping the engine and re-priming. Also, intermittent operation of the primer pump during cold engine operation did not always keep both pumps operating. Cold engine enrichment could be accomplished by adjusting the low speed screws on the injector pumps, but since these screws are not normally accessible to the operator, it required repeated stopping of the machine to re-adjust the screws. An improved starting and enrichment system for this mechanical fuel injection system was needed.
It can be seen, therefore, that primary fuel delivery systems for an engine, whether these primary systems use carburetors or fuel injection, would benefit from a supplemental fuel system which would provide the functions of starting, enrichment, and adjustment of fuel flow at low engine speeds. It would also be beneficial if one adjustment could be performed which would modify fuel flow for all engine cylinders, and it would be convenient if this adjustment could be performed by the operator while driving.
It is an object of this invention to provide a supplemental fuel delivery system for an internal combustion engine which provides additional fuel for cold starting and enrichment, and adjustment of the low speed fuel flow at normal operating conditions.
It is a further object of this invention that only a single operator adjustment of this supplemental system be required and that this single adjustment can be performed while driving.
Still further objects and advantages will become apparent from a consideration of the ensuing description and drawing.